Memory systems accumulate data errors as they operate. Errors occur in most memory systems only if addressed; however, magnetic bubble memories are an exception. Data in bubble memories are continuously circulated to maintain a substantially constant chip temperature to prevent fatigue due to temperature changes. Due to this continuous circulation errors occur at a measurable rate whether or not data is read from or written into the memory. An exerciser is utilized to correct data errors in a memory system by reading the memory, detecting any errors present in the data read, correcting any errors detected, and placing the correct data into the memory.
To ensure memory reliability it must be exercised at a rate dictated by the worst case memory error specification. If the memory is exercised at a slower rate, multiple errors which are not correctable by the exerciser may accumulate in the memory. This worst case exercise rate requires a certain percentage of system access time during which productive processing cannot be conducted. Most memory segments perform many orders of magnitude better than the worst case error specification; accordingly, if memories are exercised at such a rate, productive processing time is needlessly wasted.